1. Field of the Invention
The present invention relates to chronometers and, more specifically, to a clock that displays a continuously moving day hand.
2. The Prior Art
Clocks and other types of chronometers have an ancient lineage. Some of the earlier clocks used peg and tooth gears in order to display hours and minutes somewhat accurately. More recently, many chronometers use gear trains of toothed gears to provide this feature.
Basic gears work on the principle that when two circles are turning with their edges at the same speed, their relative rotational speeds are a function of the difference in their circumference, which are, in turn, dependent upon their respective radii or diameters, through use of the equation C=2.pi.R (or C=.pi.D). Teeth around the edges of a circular gear are often utilized to eliminate slippage between the edges of the circular gears. This guarantees that the edges of the circular gears rotate at the same speed, and that torque from one gear to another is transferred without loss. One added feature of utilizing gears is that while the relative speed of the rotation of two intermeshing gears is based on the ratio of their respective diameters, the amount of torque transferred has an inverse ratio. Thus, if a first gear has 5 teeth around its circumference, and a second gear has 30 teeth similarly spaced around its circumference, the first gear will turn 6 times as fast as the first, but have ⅙ the torque. It should also be noted that since the edges are synchronized, the two gears rotate in opposite directions when engaged.
These features have long been utilized in clocks and other chronometers. Thus, a gear driving a minute hand and one driving an hour hand can be synchronized if the gear ratios between the two have a ratio of 60/1, and this can be accomplished utilizing a 5/1 and a 12/1 gear ratio or a 10/1 and a 6/1 gear ratio.
At one point in the past, gear trains consisting single gears that engaged and intermeshed were utilized in clocks and other chronometers. However, it was discovered that multiple gears could be fixably mounted on the same shaft, and that gear trains so constructed were simpler to construct and often easier to design and took up less space. Many mechanical clocks today utilize this feature, with most of their gears in their gear trains being constructed utilizing multiple gears mounted on common shafts, and with some of those shafts being utilized to drive the hands of the chronometers.
Many, if not most, mechanical or partially mechanical clocks and other chronometers today operate by having a drive gear that operates at a fairly high constant speed. Thus, a drive gear being driven by 120 cycle current in the U.S. would typically rotate 120 times per second. This rotation would be stepped down to 1 cycle or revolution per second for a “Second” gear through use of a set of gears providing a 120/1 gear ratio. The “Second” gear could then be stepped down to a “Minute” gear through use of a set of gears providing a 60/1 gear ratio, and an “Hour” gear through use of a set of gears again providing a 60/1 gear ratio. Attaching the “Hour”, “Minute”, and “Second” gears to hollow shafts of differing sizes, inserting one of these shafts into another, and then attaching hands to the these shafts, provides the familiar clock or watch face with hour, minute, and second hands rotating around a common center.
While clocks and other chronometers have long been capable of displaying hours, minutes, and seconds, chronometers displaying days of the week are much less common. One problem that has been difficult to solve is that of setting the day of the week. When setting, in particular, the hour and minute, it is common for clocks and other chronometers to provide this feature by manually rotating the minute hand completely for each hour that needs to be changed. Thus, in order to adjust the time forward by 2 hours and 15 minutes, one might rotate the minute hand around the dial 21/4 times. While laborious, this has long been considered acceptable overhead, given that clocks rarely need to be adjusted that much. But that approach does not work well when adopted to adjusting a day hand, because in order to adjust the day and time ahead by 3 days 2 hours and 15 minutes, one would need to rotate the minute hand 741/4 times (3*24+2+¼) around the clock face. This is one of the reasons that Day hands have not been seen in the past that were driven directly and continuously off of a gear train that also directly and continuously drives the Hour, Minute, and Second hands. Rather, chronometers that display the day of the week typically utilize some type of ratchet system, where the Day hand is effectively decoupled from the Hour, Minute, and Second gears.
It would thus be advantageous for there to be a mechanical clock utilizing a gear train that continuously drives a day hand at a constant speed utilizing the same gear train that drives hour and minute hands at a constant speed.